In the field of medical treatment and graphic arts, there have been problems in working property with respect to effluents produced from wet-processing of image forming materials, and recently, reduction of the processing effluent is strongly demanded in terms of environment protection and space saving.
Accordingly, there are needed techniques regarding photothermographic materials for photographic use and which are capable of forming black images exhibiting high sharpness, enabling efficient exposure by means of a laser imager or laser image setter. As such a technique is known a thermally developable photosensitive material, which comprises a support having thereon an organic silver salt, light-sensitive silver halide grains and a reducing agent, as described in U.S. Pat. Nos. 3,152,904 and 3,487,075; and D. Morgan "Dry Silver Photographic Material" (Handbook of Imaging Materials, Marcel Dekker, Inc., page 48, 1991). No processing solution is used in this thermally developable photosensitive material (hereinafter, also referred to as a photothermographic material), enabling a simple system friendly to the environment and operators.
Since this thermally developable photothermographic material contains an organic silver salt, light-sensitive silver halide grains and a reducing agent, there are problems such that the photothermographic material not only tends to cause fogging before or during thermal development but also easily produces fog or photolytic silver (or print-out silver). Specifically, this photothermographic material, after exposure, is subjected only to thermal development at a temperature of 80 to 250.degree. C., without being further subjected to fixing so that there was such problems that silver images causes discoloring upon exposure to light or heat during storage under the concurrent presence of the silver halide, organic silver salt and reducing agent which remained in unexposed areas.
A technique for solving these problems is disclosed in JP-A 6-208192 and 8-267934 (herein, the term, JP-A means a unexamined and published Japanese Patent Application) and references cited therein. Although these disclosed techniques were effective to some extent, they were not sufficiently so as a technique to satisfy levels required by the market.